NEW YORK (Reuters Health) - Women with high blood levels of
an estrogen-like compound found in soy seem to have a lower
risk of developing breast cancer, a new study suggests.

Researchers found that among more than 24,000 middle-aged
and older Japanese women, those with the highest levels of the
compound, called genistein, were only one-third as likely as
other women to develop breast cancer over 10 years.

Genistein is one of the major isoflavones, plant compounds
found in soybeans, chick peas and other legumes that are
structurally similar to the hormone estrogen, and are believed
to bind to estrogen receptors on body cells.

ADVERTISEMENT

While some studies have linked soy consumption with a lower
risk of breast cancer, others have found no protective effect.
Some animal research, in fact, has suggested that genistein
might spur tumor development and growth. The new findings,
reported in the Journal of Clinical Oncology, suggest that this
is not the case in women, at least when genistein is consumed
through food alone.

"This finding suggests a risk-reducing rather than a
risk-enhancing effect of isoflavones on breast cancer, even at
relatively high concentrations within the range achievable from
dietary intake alone," write the researchers, led by Dr. Motoki
Iwasaki of the National Cancer Center in Tokyo.

The study included 24,226 women ages 40 to 69 who gave
blood samples and completed a dietary assessment, then were
followed for an average of 10 years. During that time, 144
women were diagnosed with breast cancer.

When Iwasaki's team separated the women based on their
blood levels of genistein at the study's start, they found that
the one-quarter with highest levels were 65 percent less likely
to develop breast cancer than the quarter of women with the
lowest genistein levels.

There was no risk reduction seen among women with moderate
levels of the isoflavone, however.

Most past studies on soy isoflavones and breast cancer have
used dietary questionnaires, Iwasaki noted. "In contrast, our
study used a direct measurement of plasma isoflavone levels,
which provides not only an index of intake but also of the
absorption and metabolism of isoflavone," the researcher told
Reuters Health.

Together with past studies, Iwasaki said, the findings
suggest that a high isoflavone intake from food may help lower
breast cancer risk.

Whether the findings necessarily extend to women in Western
countries is not clear, however. Japanese women, Iwasaki noted,
typically consume soy isoflavones on a regular basis starting
from a young age, which may influence the compounds' effects on
breast cancer development.